Showing papers in "Jetp Letters in 2005"

Modulation instability of Stokes wave → freak wave

Abstract: Formation of waves of large amplitude (freak waves, killer waves) at the surface of the ocean is studied numerically. We have observed that freak waves have the same ratio of the wave height to the wave length as limiting Stokes waves. When a freak wave reaches this limiting state, it breaks. The physical mechanism of freak wave formation is discussed.

Magnetoelectric effects in gadolinium iron borate GdFe3(BO3)(4)

Abstract: Magnetoelectric interactions have been investigated in a single crystal of gadolinium iron borate GdFe3(BO3)4, whose macroscopic symmetry is characterized by the crystal class 32. Using the results of this study, the interplay of magnetic and electric orderings occurring in the system has been experimentally revealed and theoretically substantiated. The electric polarization and magnetostriction of this material that arise in spin-reorientation transitions induced by a magnetic field have been investigated experimentally. For H ‖ c and H ⊥ c, H-T phase diagrams have been constructed, and a strict correlation between the changes in the magnetoelectric and magnetoelastic properties in the observed phase transitions has been ascertained. A mechanism of specific noncollinear antiferroelectric ordering at the structural phase transition point was proposed to interpret the magnetoelectric behavior of the system within the framework of the symmetry approach in the entire temperature range. This ordering provides the conservation of the crystal class of the system when the temperature decreases to the antiferroelectric ordering point. The expressions that have been obtained for the magnetoelectric and magnetoelastic energy describe reasonably well the behavior of gadolinium iron borate observed experimentally.

Detonation in an aluminum-teflon mixture

Abstract: Detonation in an aluminum-fluoroplastic-4 (Teflon) mixture is studied experimentally. To increase reactivity, the initial mixture is pretreated in a mechanochemical activator. As a result, a mechanically activated composite is obtained in the form of thin aluminum layers in a Teflon matrix. The action of a shock wave on a composite sample initiates the steady detonation regime, in which the initial and final substances are in the condensed state. Depending on the percentage composition and density of the mixture, the detonation velocity varies from 700 to 1300 m/s for the speed of sound below 100 m/s in the initial composition. The steady detonation velocity changes insignificantly when sample pores are filled with helium instead of air. The results prove that it is possible in principle to reach the steady detonation regime in reactive condensed mixtures forming final reaction products in the solid state.

Mesoscopic wave turbulence

Abstract: We report results of simulation of wave turbulence. Both inverse and direct cascades are observed. The definition of “mesoscopic turbulence” is given. This is a regime when the number of modes in a system involved in turbulence is high enough to qualitatively simulate most of the processes but significantly smaller than the threshold, which gives us quantitative agreement with the statistical description, such as the kinetic equation. Such a regime takes place in numerical simulation, in essentially finite systems, etc.

Inflaton field potential producing an exactly flat spectrum of adiabatic perturbations

Abstract: Presented in this letter is the exact solution of the problem of finding the potential of an inflaton scalar field for which adiabatic perturbations generated during a de Sitter (inflationary) stage in the early Universe have an exactly flat (or, the Harrison-Zeldovich) initial spectrum. This solution lies outside the scope of the slow-roll approximation and higher-order corrections to it. The potential found depends on two arbitrary physical constants, one of which determines the amplitude of the perturbations. For small (zero) values of the other constant, a long (infinite) inflationary stage with slow rolling of the inflaton field exists.

Measurement of the Pion Form Factor in the Range 1.04 1.38 GeV with the CMD-2 Detector

Abstract: The cross section for the process e + e − → π+π− is measured in the c.m. energy range 1.04—1.38 GeV by analyzing 995 000 selected collinear events including 860000 e + e − events, 82000 μ+μ− events, and 33000 π+π− events. The systematic and statistical errors of measuring the pion form factor are equal to 1.2–4.2 and 5–13%, respectively.

On the unique possibility of significantly increasing the contrast of dark resonances on the D1 line of 87Rb

Abstract: We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for the D1 line of alkali atoms with nuclear spin I = 3/2 by bichromatic linearly polarized light (lin‖lin field) under the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for the D1 line of 87Rb.

EPR identification of the triplet ground state and photoinduced population inversion for a Si-C divacancy in silicon carbide

Abstract: It is shown that intrinsic defects responsible for the semi-insulating properties of SiC represent Si-C divacancies in a neutral state (VSi-VC)0, which have the triplet ground state. The energy level scheme and the mechanism of creating the photoinduced population inversion of the triplet sublevels of the divacancy ground state are determined. It is concluded that there is a singlet excited state through which spin polarization is accomplished, and this fact opens the possibility of detecting magnetic resonance on single divacancies.

Observation of the elastic quasi-mosaicity effect in bent silicon single crystals

Abstract: A considerable elastic quasi-mosaicity effect has been observed upon the diffraction of x-rays on a bent silicon single-crystal plate. It has been shown that the effect depends on the choice of reflecting crystallographic planes and the orientation of the plate cut. The effect can be applied to improve the characteristics of silicon single-crystal monochromators of electromagnetic radiation and silicon single-crystal deflectors of charged-particle beams.

Ground-state properties of a one-dimensional system of dipoles

Abstract: A one-dimensional (1D) Bose system with dipole-dipole repulsion is studied at zero temperature by means of a quantum Monte Carlo method. It is shown that, in the limit of small linear density, the bosonic system of dipole moments acquires many properties of a system of noninteracting fermions. At larger linear densities, a variational Monte Carlo calculation suggests a crossover from a liquidlike to a solidlike state. The system is superfluid on the liquidlike side of the crossover and is normal deep on the solidlike side. Energy and structural functions are presented for a wide range of densities. Possible realizations of the model are 1D Bose atomic systems, with permanent dipoles or dipoles induced by static field or resonance radiation; or indirect excitons in coupled quantum wires; etc. We propose parameters of a possible experiment and discuss manifestations of the zero-temperature quantum crossover.

Destruction of the Fermi surface due to pseudogap fluctuations in strongly correlated systems

Abstract: We generalize the dynamical-mean field theory (DMFT) by including into the DMFT equations dependence on the correlation length of the pseudogap fluctuations via the additional (momentum dependent) self-energy Σk. This self-energy describes nonlocal dynamical correlations induced by short-ranged collective SDW-like antiferromagnetic spin (or CDW-like charge) fluctuations. At high enough temperatures, these fluctuations can be viewed as a quenched Gaussian random field with finite correlation length. This generalized DMFT + Σk approach is used for the numerical solution of the weakly doped one-band Hubbard model with repulsive Coulomb interaction on a square lattice with nearest and next nearest neighbor hopping. The effective single impurity problem is solved by using a numerical renormalization group (NRG). Both types of strongly correlated metals, namely, (i) doped Mott insulator and (ii) the case of the bandwidth W ≲ U (U-value of local Coulomb interaction) are considered. By calculating profiles of the spectral densities for different parameters of the model, we demonstrate the qualitative picture of Fermi surface destruction and formation of Fermi arcs due to pseudogap fluctuations in qualitative agreement with the ARPES experiments. Blurring of the Fermi surface is enhanced with the growth of the Coulomb interaction.

Parton distribution functions from the precise NNLO QCD fit

Abstract: We report on the parton distribution functions (PDFs) determined from the NNLO QCD analysis of the world inclusive DIS data with account for the precise NNLO QCD corrections to the evolution equations kernel. The value of the strong coupling constant α s NNLO (M Z ) = 0.1141 ± 0.0014 (exp.), in fair agreement with the one obtained using the earlier approximate NNLO kernel by van Neerven-Vogt. The intermediate bosons rates calculated in the NNLO using the obtained PDFs are in agreement with the latest Run II results.

Heavily-chirped solitary pulses in the normal dispersion region: New solutions of the cubic-quintic complex Ginzburg-Landau equation

Abstract: A new type of the heavily-chirped solitary pulse solutions of the nonlinear cubic-quintic complex Ginzburg-Landau equation has been found. The methodology developed provides for a systematic way to find the approximate but highly accurate analytical solutions of this equation with the generalized nonlinearities within the normal dispersion region. It is demonstrated that these solitary pulses have the extra-broadened parabolic-top or fingerlike spectra and allow compressing with more than a hundredfold growth of the pulse peak power. The obtained solutions explain the energy scalable regimes in the fiber and solid-state oscillators operating within the normal dispersion region and promise to achieve microjoules femtosecond pulses at MHz repetition rates.

On differential equation on four-point correlation function in the conformal Toda field theory

Abstract: The properties of completely degenerate fields in the conformal Toda field theory are studied. It is shown that a generic four-point correlation function that contains only one such field does not satisfy an ordinary differential equation, in contrast to the Liouville field theory. Some additional assumptions for other fields are required. Under these assumptions, we write such a differential equation and solve it explicitly. We use the fusion properties of the operator algebra to derive a special set of three-point correlation functions. The result agrees with the semiclassical calculations.

Specificity of magnetoelectric effects in a new GdMnO3 magnetic ferroelectric

Abstract: A complex study of the magnetic, electric, magnetoelectric, and magnetoelastic properties of GdMnO3 single crystals has been performed in the low-temperature region in strong pulsed magnetic fields up to 200 kOe. An anomaly of the dielectric constant along the a axis of a crystal has been found at 20 K, where a transition from an incommensurate modulated phase to a canted antiferromagnetic phase, as well as electric polarization along the a and b axes of the crystal induced by the magnetic field H‖ b (Hcr ∼ 40 kOe), is observed. Upon cooling the crystal in an electric field, the magnetic-field-induced electric polarization changes its sign depending on the sign of the electric field. The occurrence of the electric polarization is accompanied by anisotropic magnetostriction, which points to a correlation between the magnetoelectric and magnetoelastic properties. Based on these results, it has been stated that GdMnO3 belongs to a new family of magnetoelectric materials with the perovskite structure.

Pure Spin Photocurrents in Low-Dimensional Structures

Abstract: As is well known, the absorption of circularly polarized light in semiconductors results in optical orientation of electron spins and helicity-dependent electric photocurrent, and the absorption of linearly polarized light is accompanied by optical alignment of electron momenta. Here, we show that the absorption of unpolarized light leads to the generation of a pure spin current, although both the average electron spin and electric current vanish. We demonstrate this for direct interband and intersubband as well as indirect intraband (Drude-like) optical transitions in semiconductor quantum wells.

Variable-range cotunneling and conductivity of a granular metal

Abstract: The Efros-Shklovskii (E-S) law for the conductivity of granular metals is interpreted as a result of a variable-range cotunneling process. The cotunneling between distant resonant grains is predominantly elastic at low T ≤ T c , while it is inelastic (i.e., accompanied by creation of electron-hole pairs on a string of intermediate non-resonant grains) at T ≥ T c . The corresponding E-S temperature T ES , in the latter case, is slightly (logarithmically) T dependent. The magnetoresistance in the two cases is different: it may be relatively strong and negative at T≪T c , while, at T > T c , it is suppressed due to inelastic processes, which destroy the interference.

Universal Statistics of the Local Green's Function in Wave Chaotic Systems with Absorption ¶

Abstract: We establish a general relation between the statistics of the local Green’s function for systems with chaotic wave scattering and uniform energy loss (absorption) and the two-point correlator of its resolvents for the same system without absorption. Within the random matrix approach, this kind of a fluctuation dissipation relation allows us to derive the explicit analytic expression for the joint distribution function of the real and imaginary part of the local Green’s function for all symmetry classes as well as at an arbitrary degree of time-reversal symmetry breaking in the system. The outstanding problem of orthogonal symmetry is further reduced to simple quadratures. The results can be applied, in particular, to the experimentally accessible impedance and reflection in a microwave cavity attached to a single-mode antenna.

Phase transition with suppression of magnetism in BiFeO3 at high pressure

Abstract: The magnetic behavior of a Bi57FeO3 powdered sample was studied at high pressures by the method of nuclear forward scattering (NFS) of synchrotron radiation. The NFS spectra from 57Fe nuclei were recorded at room temperature under high pressures up to 61.4 GPa, which were created in a diamond anvil cell. In the pressure interval 0 < P < 47 GPa, the magnetic hyperfine field H Fe at the 57Fe nuclei increased reaching a value of ∼52.5 T at 30 GPa, and then it slightly decreased to ∼49.6 T at P = 47 GPa. As the pressure was increased further, the field H Fe abruptly dropped to zero testifying a transition from the antiferromagnetic to a nonmagnetic state (magnetic collapse). In the pressure interval 47 < P < 61.4 GPa, the value of H Fe remained zero. The field H Fe recovered to the low-pressure values during decompression.

Bound states of three and four resonantly interacting particles

Abstract: We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonance bound state of two fermions in a spin-singlet state, with corresponding scattering length a F . Applying this approach to the calculation of the dimmer-dimer scattering length a B , we recover exactly the already known result a B = 0.6 a F . We use the developed approach to obtain new results in 2D for fermions and bosons. Namely, we calculate bound state energies for three bbb and four bbbb resonantly interacting bosons in 2D. For the case of resonance interaction between fermions and bosons, we exactly calculate bound state energies of the following complexes: two bosons plus one fermion bbf, two bosons plus two fermions bf↑bf↓, and three bosons plus one fermion bbbf.

Spin-dependent recombination in GaAsN solid solutions

Abstract: Room-temperature spin-dependent recombination in a series of GaAs1−x Nx solid solutions (x = 2.1, 2.7, 3.4%) has been observed as manifested by a more than threefold decrease in intensity of the edge photoluminescence upon switching from circular to linear polarization of the exciting light or upon the application of a transverse magnetic field (∼300 G). The interband absorption of the circularly polarized light is accompanied by the spin polarization of conduction electrons, which reaches 35% with an increase in the pumping level. The observed effects are explained in terms of the dynamic polarization of deep paramagnetic centers and the spin-dependent trapping of conduction electrons on these centers. The electron spin relaxation time, as estimated from the dependence of the edge photoluminescence depolarization in the transverse magnetic field (the Hanle effect) on the pumping intensity, is on the order of 1 ns. According to the adopted theory, the electron spin relaxation time in the presence of spin-dependent recombination is determined by a slow spin relaxation of localized electrons. The sign (positive) of the g factor of localized electrons has been experimentally determined from the direction of the magnetic-field-induced rotation of their average spin observed in the three GaAsN crystals studied.

X-ray detected magnetic resonance at the Fe K-edge in YIG: Forced precession of magnetically polarized orbital components

Abstract: X-ray detected magnetic resonance (XDMR) has been measured for the first time on exciting the Fe K-edge in a high-quality yttrium iron garnet film epitaxially grown on a gadolinium gallium garnet substrate. This challenging experiment required resonant pumping of yttrium iron garnet at high microwave power, i.e., in the foldover regime. X-ray magnetic circular dichroism (XMCD) was used to probe the change in the longitudinal component of the magnetization M Z induced by the precession of magnetic moments located at the iron sites. Since XMCD at the Fe K-edge refers mostly to the equilibrium contribution of magnetically polarized 4p orbital components, XDMR at the Fe K-edge should reflect the precessional dynamics of the latter orbital moments. From the measured precession angle, we show that there is no dynamical quenching of the polarized orbital components at the iron sites in yttrium iron garnet.

Merging gauge coupling constants without grand unification

Abstract: The merging of the running coupling constants of the weak, strong, and electromagnetic fields does not require the unification of these gauge fields at high energy. It can, in fact, be the property of a general fermionic system in which gauge bosons are not fundamental.

Increase in radiation intensity in a quasi-spherical ``double liner''/``dynamic hohlraum'' system

Abstract: A concept of the magnetic implosion of quasi-spherical liners, concentration of their kinetic energies, conversion of energy into thermal radiation, confinement of its energy in the cavity of an emitting plasma shell in the “double liner”/“dynamic hohlraum” system, and the irradiation of a spherical target is proposed for the physics of high energy densities and inertial confinement fusion. The radiation intensity on the target was shown to increase considerably due to capture of radiation in the process of converting the kinetic energy of the liner into radiation. The dynamics of the liners and the generation of radiation are simulated by the ZETA code using a physical model developed for a nonequilibrium plasma in a cylindrical geometry. The effect of the instability and inhomogeneity of the liners on confinement of radiation energy is estimated.

Optical and magneto-optical studies of a multiferroic GaFeO3 with a high Curie temperature

Abstract: Single crystals of a noncentrosymmetric orthorhombic pyroelectric ferrimagnet Ga2−x FexO3 with a Curie temperature within 260–345 K have been grown by the flux method. It has been found that the electrical properties of the single crystals varied over a broad range from 105 to 1013 Ω cm depending on the presence of transitionmetal oxide impurities. The dispersion relations for all three principal dielectric functions of orthorhombic GaFeO3 have been determined in the range 0.7–5.4 eV by spectroscopic ellipsometry. The spectra of the dielectric functions of the orthorhombic Ga2−x FexO3 crystals are compared with the spectra of the trigonal crystals. The Faraday effect and second-harmonic generation are studied, and the law of the transition to the paramagnetic state has been determined. The crystallographic and magnetic contributions to the second-harmonic generation are analyzed.

Generation of an attosecond X-ray pulse in a thin film irradiated by an ultrashort ultrarelativistic laser pulse

Abstract: The possibility of generating an attosecond x-ray pulse in a thin solid-density plasma layer irradiated by a femtosecond laser pulse of ultrarelativistic intensity has been demonstrated in numerical simulation. Changes in the plasma layer parameters during the light pulse result in the generation of a wide, partly continuous radiation spectrum in the layer. The separation of limited parts in the reflected or transmitted light spectrum makes it possible to obtain isolated short electromagnetic pulses with an intensity reaching 1% of the exciting light intensity.

Features of dusty structures in the upper Earth's atmosphere

Abstract: The features of the Earth’s dusty ionosphere are considered using as an example the summer polar mesosphere. The effect of the optical properties of microparticles on their heating and photoelectron emission under the action of solar radiation is analyzed in detail. Certain photochemical consequences of the presence of dust in the upper atmosphere are studied. In particular, it is shown that microparticles can noticeably reduce the concentration of water vapor in the upper atmosphere and this decrease in turn limits the particle sizes. The influence of the effect under consideration on the behavior of the charged component of the upper atmosphere is discussed.

Generation of Terahertz radiation upon the optical breakdown of a gas

Abstract: Terahertz radiation of plasma oscillations excited upon the optical (axicon) breakdown of a gas in the presence of external fields of other frequency ranges has been analyzed. It has been shown that the spectra and intensity of oscillations and radiation generated by them depend strongly on the character of the spatiotemporal evolution of the formed plasma. The intensity is maximal upon the rapid formation of the plasma with a sharp boundary and decreases to very low values for objects with a smooth density profile. New schemes and regimes of break-down have been proposed, which make possible, according to preliminary estimates, an emitted energy of about 10 mJ with moderate intensities of ionizing laser radiation.

Influence of the Orientation of a Crystal on Thermal Polarization Effects in High-Power Solid-State Lasers

Abstract: The polarization thermal self-action of laser radiation propagating in an isotropic crystal has been studied experimentally. New nonlinear effects have been observed for the first time. These effects include a change in the symmetry of the depolarized-field distribution and the qualitative dependence of the degree of the self-induced depolarization on the geometry of the beam and crystal. The classical problem of self-induced depolarization has been analytically solved in the general form for an arbitrary orientation of any cubic crystal. The theoretical results agree well with the experimental data. The optimum orientation of the laser crystal has been determined, which can be effectively used in lasers with high average power.

Hydraulic jump as a white hole

Abstract: In the geometry of the circular hydraulic jump, the velocity of the liquid in the interior region exceeds the speed of the capillary-gravity waves (ripplons), whose spectrum is “relativistic” in the shallow water limit. The velocity flow is radial and outward, and thus the relativistic ripplons cannot propagate into the interior region. In terms of the effective 2 + 1 dimensional Painleve-Gullstrand metric appropriate for the propagating ripplons, the interior region imitates a white hole. The hydraulic jump represents the physical singularity at the white-hole horizon. The instability of the vacuum in the ergoregion inside the circular hydraulic jump and its observation in recent experiments on superfluid 4He by Rolley et al. [3] are discussed.